1. Field of the Invention
The present invention relates to antenna devices preferably for use in near field communication (NFC) systems and so forth and to electronic appliances equipped with such an antenna device.
2. Description of the Related Art
In mobile communication appliances such as cellular phone terminals and tablet PCs, mounting of communication circuits corresponding to HF band communication systems such as an NFC system has been progressing.
In addition, profile reduction has also been progressing in recent mobile communication appliances and it has become increasingly common to reinforce the strength of such appliances through “metallization” of the casing by, for example, performing a magnesium plating treatment on a resin casing or using a metal casing such as an aluminum body in order to deal with strength deficiencies caused by such profile reduction.
However, in an electronic appliance that includes a metal casing, there are problems in that it becomes impossible to perform communication with a communication partner or the communication range is markedly degraded since a built-in antenna coil is shielded by the metal.
Consequently, electronic appliances are known that include a metal casing having an opening and a slit formed therein as a radiating body such as disclosed in Japanese Patent No. 4993045.
Electronic appliances equipped with a communication circuit often include a wide planar conductor surface in order to electromagnetically shield high-frequency circuits and electrostatically shield flat panel displays, and also to stabilize a reference potential of a touch panel.
However, in electronic appliances equipped with a wide planar conductor surface inside the casing, the antenna coil inside the casing is shielded by the conductor surface. If an opening and a slit are formed in the conductor surface in order to avoid such shielding, the original shielding property and the stability of the electrical potential are degraded.
Furthermore, if the opening and the slit are at a position where they are visible from the outside, there may also be a restriction from the viewpoint of design.